In line with the recent spread of the use of HDMI (Trademark) as a digital interface for connecting devices, baseband signals are increasingly being used for connecting multiple devices for transmitting digital data with high picture and sound quality. Each device is often installed with its own high picture quality circuit or high sound quality circuit. However, each high picture quality circuit and high sound quality circuit is designed to achieve the optimal picture quality and optimal sound quality by each device alone. Accordingly, when picture or sound is output after going through multiple devices, the optimal picture quality and sound quality are not always output.
In particular, a display device, which is a signal-receiving unit, often adaptively switches circuits depending on whether each frame or a part of the frame is a still picture or motion picture. However, a still picture or motion picture is determined only based on the video information received. Accordingly, erroneous detection may occur depending on the determination algorithm and picture property, resulting in below optimal picture quality.
As a measure for improving this point, the next system is proposed when multiple devices are connected by a bi-directional bus such as IEEE1394 (Trademark). The proposed system is to determine which device should operate which function by making each device retain attribute information that indicates whether processing is feasible by the device and comparing the availability of decoding.
However, in the above system, the entire system cannot be controlled optimally based on selection of each function for outputting the highest picture quality and highest sound quality in a transmitting device and receiving device. In addition, the above system is not feasible to correctly determine a motion picture and still picture based on the accuracy of a frame or a part of the frame in processing at the receiving device.
Furthermore, the above system results in duplicate processing if video signals and audio signals are processed in both transmitting device and receiving device. This results in an increased load on the entire system including the transmitting device and receiving device. The above system has these disadvantages.    [Patent Document 1] Japanese Patent Unexamined Publication No. H11-187034    [Nonpatent Document 1] HDMI standard, Specification Version 0.9, 1.0, and 1.1 of High Definition Multimedia Interface